This invention relates to a withdrawal system for a vessel containing solid particulate material and in particular, to a vessel utilized for blending particulate material such as plastic pellets.
Blenders to which the present invention relates have been generally known and include a vertically oriented vessel having a inlet for particulate material and an outlet for particulate material. The outlet for discharging the particulate material from the vessel is positioned in the conical bottom of the vessel. As a blender, the device may have a system for recirculating or mixing material within the vessel to achieve blending. This recirculation means may be the form of a centrally located vertical lift pipe inside the vessel. Gaseous fluid under pressure may be supplied to the bottom of the vessel below the lower end of the lift pipe. As the gaseous fluid under pressure is supplied to the bottom of the vessel it entrains the particulate material near the bottom of the vessel and lifts it up through the lift column where it is discharged from the outlet of the lift column in a geyser like manner onto the top of the vessel. As a result, material circulates from the top of the vessel down to the bottom of the vessel by gravity and then is lifted by the gas under pressure back up to the top.
Since it is desirable to have a high velocity gas stream at the bottom of the vessel for entraining the particulate material in the bottom thereof for lift up through the column, it would be desirable to provide a smaller opening at the bottom of the vessel. This will enable a lower volume and pressure gas to be used to circulate material through the lift column thereby decreasing energy consumption. However, when it is desired to withdraw material from the vessel, it is desired to do so at a rapid rate, and to accomplish this it would be desirable to provide a large opening at the outlet of the vessel. While separate gas inlets or nozzles could be provided, these have not proved to be entirely satisfactory.